Upper Blue Lake Dam Seismic Retrofit Project

Our firm first investigated the existing condition of the dam to determine seismic vulnerabilities and anticipated deformations. We then designed a stability buttress to mitigate against potential hazards. Regulators were also concerned with the stability of a stacked mortared rock wall that makes up the downstream shell of the dam at the tallest section; stability analyses allayed those concerns, however. Excavation for the buttress foundation was made down to bedrock to provide solid support after groundwater infiltration was found to affect the integrity of on-site soil.

Building the buttress required the demolition of the existing intake structure and construction of a new one approximately 50 feet further upstream, which included extending the two low-level outlet (LLO) pipes. The team used poured concrete to create the new structure’s foundation slab and walls, and the encasement of the LLO pipes. As part of the design, a drawdown analysis was performed to accurately account for the outflow capabilities of the new LLO system, ensuring compliance with California Division of Safety of Dams requirements.